Peter -
1. I have heard about the application of moxa to the skin as a form of discipline for unruly kids, once upon a time. Not on the nails, for whatever that's worth. There is no doubt that warrior cultures are usually very harsh to their male children, and this helps produce warriors. I have never read of a warrior culture where this is not true.
2. I recall Turnbull's books - the first one being delightful, and the 2nd anything but. As I recall, there was a lot of controversy about The Mountain People. As best I remember, other anthropologists asserted that the Ik's "culture" was an outcome of a) a severe famine b) an utter disruption of a stable way of life by resettlement and the government's destruction of their traditional way of life, and that, Turnbull ended up "blaming the victims," so to speak.
3. One problem with almost all studies of culture, including cultural relativism is that history and culture are written by the ruling class - as is the rationalizing of the culture. It is hard to even get access to those violated and abused in the culture. For example, there was recently a long radio essay about a woman with an African father and African-American mother, who, married in the US, wished to go back to Kenya for a second wedding, so her children would be able to appreciate and love both cultures. At first glance, she had entered a different and wonderful culture. But as she got to know the women, she learned that every woman, on the way home from school, or somewhere else, had been kidnapped and raped. Afterwards, the man would present himself to the family with this accomplished fact of possession and then the girl would be married to him. As Edgerton points out (yes, you have the right book), many anthropologists would find an elegant intellectual rationalization for this, so that, somehow, it would not be "rape" and "kidnapping." But the woman found, as she got to know each of the women of the culture, that they suffered in silence, and everyone of them experienced this as a rape and violation, even though the conventions of their culture did not give them a public language to say so.
4. Thus, in sum, I deliberately chose the word "torture." Why? Because that is the child's experience, and I have long felt that Sokaku has had his voice stolen. Yes, that's dramatic. But for a long time, my work (and my life) revolved around abused children - from many cultures - and although each culture had a different explanation for the physical infliction of pain and/or sexual exploitation of their young, the children, as best I could tell, experienced the pain exactly the same. To be sure, as they grew up, the explanations the culture provided - or the desperate measures the child took to accept the abuse ("I deserved it," for example), might differ. But the core experience was the same. However, we could not predict from that core experience how the child would grow up. We could generalize that it was more likely that - - - but the wonder of humanity is that each of us will break free of the bounds of such predictions (which Emanuel Levinas would refer to as "totalizing").
So, on the one hand, I do think it is very important to ascertain the larger cultural context - how such actions as the infliction of pain upon one's child were viewed. On the other, the child's raw, core experience must not be forgotten - and the victim of violence, be it the child or the woman who is beaten - often is.
5. Finally, the type of psychology I hew to is referred to as phenomenological or individualized psychology. Rather than trying to find a norm, in which one can profile (if x happens to a child, y will develop), which results, usually, in superficial generalizations, one views each individual as unique. If x happened to this child, y resulted for this child). On the one hand, one is left with a tautology, but on the other, it is the truth. One young man I know was brought up by an Army Intelligence officer who decided, as an experiment, to see if he could psychologically destroy his son, through physical and psychological torture. (That word again). He, now a man of 35, described to me, pleading with his father as he was tortured, saying, "You are supposed to take care of me. You are not supposed to do this." How did he turn out? Is he an abuser himself? A torturer? In fact, his response was to become a man who tried never to reveal his feelings, because every revelation of such resulted in his father using it to create more pain and also, a militant pacifism. He will literally accept death rather than do anything violent to anyone. It makes sense as a narrative - but there is no way we could predict that such a man would emerge from such a background.
By way of saying, all I've tried to do is tell, as best I can, what I believe to be Takeda's story, to understand if there was anything in his early life which could help make sense how such a man could have developed. Rather than the "type" - (a typical example of a feudal samurai, as some have asserted) - I wanted the man. And perhaps I am lacking a little humility, but I believe I explain his character - the inability to settle, the prickly defensiveness and paranoia, his relationship (close/far) with his deshi, the way he brought up (and didn't bring up) his own son, who would not refer to him as "father," but rather "Takeda Sensei," with more truth than has been done previously.
Best
Ellis